Worksites, for example, mine sites, landfills, quarries, construction sites, etc., commonly undergo geographic alteration by machines performing various tasks thereon. For example, at a coal mining site, mounds of coal are continually moved by dozers about the site, onto conveyors, into chutes, and to prepare the coal for transport. Likewise, at an excavation site, terrain is altered by digging, grading, leveling, or otherwise preparing the terrain for various uses. During the performance of these tasks, the machines can operate in situations that are hazardous to an operator, under extreme environmental conditions, or at work locations remote from civilization. Accordingly, autonomous or semiautonomous machines are often utilized.
In order to achieve autonomy, a machine must be able to accurately determine its position relative to its environment at all times. The positioning of a mobile machine, such as earth moving equipment, mining equipment, and railroad equipment is commonly achieved using known reference-based systems, such as the Global Navigation Satellite Systems (GNSS). The GNSS comprises a group of satellites that transmit encoded signals, and receivers on the ground. The receivers may use trilateration techniques to calculate their position using the travel time of the satellites' signals and information about the satellites' current location.
Currently, the most popular form of GNSS for obtaining absolute position measurements is the global positioning system (GPS), which is capable of providing accurate position information provided that there is sufficient satellite coverage. However, where the satellite signal becomes disrupted or blocked such as, for example, in urban settings, tunnels and other GNSS-degraded or GNSS-denied environments, a degradation or interruption or “gap” in the GPS positioning information can result.
In order to achieve more accurate, consistent and uninterrupted positioning information, GNSS information may be augmented with additional positioning information obtained from complementary positioning systems. Such systems may be self-contained and/or “non-reference based” systems within the platform, and thus need not depend upon external sources of information that can become interrupted or blocked. One such “non-reference based” or relative positioning system is the inertial navigation system (INS). Inertial sensors are self-contained sensors within the platform that use gyroscopes to measure the platform's rate of rotation/angle, and accelerometers to measure the platform's specific force (from which acceleration is obtained). Using initial estimates of position, velocity and orientation angles of the moving platform as a starting point, the INS readings can subsequently be integrated over time and used to determine the current position, velocity and orientation angles of the platform. Typically, measurements are integrated once for gyroscopes to yield orientation angles and twice for accelerometers to yield position of the platform incorporating the orientation angles. Thus, the measurements of gyroscopes will undergo a triple integration operation during the process of yielding position. Inertial sensors alone, however, are unsuitable for accurate positioning because the required integration operations of data results in positioning solutions that drift with time, thereby leading to an unbounded accumulation of errors.
An exemplary system that provides position monitoring is disclosed in U.S. Pat. No. 7,831,362 issued to Ishibashi et al. on Nov. 9, 2010 (“the '362 patent”). Specifically, the '362 patent discloses a machine equipped with a GPS system for measuring the location of the machine's body. Sometimes, however, the GPS measurement of the machine body's location is inaccurate. As such, the '362 patent also discloses a reference GPS that may be located away from the machine to provide measurements that may be used to correct the other GPS measurements.
Although the '362 patent may account for inaccuracies in a GPS measurement of a machine, it does not address possible inaccuracies in the location of the reference GPS, or inaccuracies in the output from the reference GPS. The sensors may also malfunction under harsh worksite conditions and render the '362 system unable to correct location inaccuracies and provide accurate position information for autonomous control of the machine.
The disclosed system for determining the position of a mobile machine is directed to overcoming one or more of the problems set forth above and/or other problems of the prior art.